1. Field of the Invention
This invention relates to the art of transforming rough diamonds into faceted, brillianteered diamonds, and, more particularly, relates to a method for cutting and faceting diamonds in such a way that the yield obtained in the finished product is significantly increased over yields previously obtained by existing cutting and faceting techniques.
2. Description of the Prior Art
The art of polishing facets on gemstones (other than diamonds) has been around for many centuries. The first known attempt to facet a diamond is believed to have taken place in the eleventh century. At that time, eight triangular faces were polished in the rough diamond, creating what became known as the “point, cut”, which resembled a pair of pyramids joined at their bases.
In the early part of the fourteenth century, a single, horizontal planar facet was introduced, which became known as the “table”, leaving four natural beveled surfaces that created the crown. Further refinement of this elemental configuration has resulted in, among others, the round brilliant cut, which is the most popular faceting configuration for today's diamonds.
Currently, diamonds are first cut into a top or crown and a bottom, base or pavilion, and a girdle lying between the two in a horizontal plane. Anywhere from four to sixteen sections (top primary facets) are cut into the top section, oriented at roughly 34.5° above horizontal. Anywhere from four to sixteen sections (bottom primary facets) are also cut into the bottom, oriented at roughly 40.75° below horizontal. This phase of the cutting process is known as “blocking”. It is almost universally accepted that these proportions and angles for brilliant cut diamonds are necessary to produce maximum brilliancy with a high degree of dispersion or “fire”. Thereafter, additional facets are added to the top and bottom sections in a second phase known as brillianteering. This approach is shown in FIGS. 1 and 2. FIG. 1 shows a stone with eight main facets in the crown and eight main facets in the pavilion (i.e. after the rough has been “blocked”), while FIG. 2 shows the same stone after brillianteering facets have been added.
Eventually, stone cutters became aware of and began to understand the effects of refraction and reflection on the optical path of light within the gem and how to control it through angles, surfaces and proportions. As the art of gem cutting evolved, it has become widely accepted that the brilliant cut is the optimal cut for simultaneously maximizing the fire, lustre, scintillation and brilliance of the stone. Since, in general, the stone is viewed by looking down at the table and crown facets, it is desirable to induce the maximum amount of light possible through the table and crown facets, down into the stone where it is reflected off of the interior surfaces of the base facets across to the opposite base facets and then back out through the table and crown facets to the viewer. The more optimal the configuration of the stone, the more even, intense and uniform is the thus reflected dome of light perceived by the viewer.
Diamonds have various characteristics that distinguish them from other gemstones. One characteristic is brilliance, which can be further categorized into external and internal. External brilliance, also referred to as lustre, generally refers to the amount of light that impinges on the top of the stone and reflects back, rather than light that enters the stone. Internal brilliance is determined by the light rays that enter the crown and reflect off the base facets and back out through the top or crown as amplified (i.e. focused) light.
Another characteristic of a diamond is dispersion, also known as fire, which is a measure of how much the white light is broken up into the spectral colors. A ray of white light striking a prism will be split up into component colors of red, orange, yellow, green, blue, indigo and violet. Dispersion is maximized when a ray of light is reflected totally from base facets and strikes the ground facets at the greatest possible angle. Dispersion is observed when a diamond moves relative to an observer.
Another characteristic of a diamond is scintillation, which is an indication of the different light patterns obtained when the stone is moved under light. Expressed in another way, scintillation is the quantity of flashes observed from the diamond when either the diamond, light source or observer moves.
The refraction index for a diamond is 2.417, which is the highest for a transparent natural gem. The amount of dispersion of light, or fire, depends on the original angle of incidence and the distance the light travels inside the stone. The larger the angle of incidence, the larger the amount of refraction within the stone, and the greater the dispersion. White light is a blend of the spectral colors and because each color slows and bends differently this causes the light to disperse into spectral colors, which creates the fire within the diamond.
Today's diamond consumer is typically a highly discriminating and well educated shopper, looking for the highest value out of his or her investment. At the same time, the diamond supplier wants to obtain the highest yield from a given piece of rough. Currently, 10%-50% retention is good for a brilliant cut diamond. Since the price per carat increases exponentially in proportion to the carat weight of a particular stone, it is highly desirable to increase the yield, and conversely decrease the waste, from a given rough. The same light and dispersion can be obtained at less cost through weight retention during the faceting process.
In the past, however, the yield obtained in creating a faceted stone has been unnecessarily limited due to the belief that, in order to obtain acceptable light dispersion (i.e. reflection and refraction), the angle of the base facets should not exceed 43%.
Thus, the desire for weight retention has given way to what has been believed to be the need to keep the angle of the base or pavilion facets in a range of between 38° and 43° relative to a horizontal plane. The result of this practice is that, in order to cut the base facets at the presently specified range of angles between 36° and 43°, an unnecessary amount of waste occurs during cutting of the stone, including unnecessarily limiting the diameter of the finished product.
Therefore, it is desirable to present a method for creating a higher yield diamond which exhibits virtually identical visual effects and light performance as today's modern or brilliant cut.
One attempt at increasing the weight of diamonds utilized a greater table spread (the ratio of the table diameter to the girdle diameter). However, it was found that the circumferential surface of the girdle would be reflected off of the base facets through the table, creating what is know as the “fish-eye” effect. Attempting to decrease the base facet angle to prevent this unwanted effect deleteriously affected the stone's fire.
U.S. Pat. No. 5,970,744 to Greeff and assigned to Tiffany and Company is directed to a cut cornered mixed-cut square gemstone having a two-step crown, a girdle, and a pavilion. The pavilion sides and corners are defined by eight rib lines which extend continuously from the girdle to the culet. The first crown step has an angle of about 41°-44° relative to the girdle plane and the angle of the second crown step is about 36° to 39° to the girdle plane. The rib lines in the pavilion are preferably at an angle of between 38°-42° relative to the girdle plane.
U.S. Pat. No. 5,657,646 to Rosenberg discloses a new cut for a precious or semi-precious jewel having two or more culets and at least one additional facet extending from the end of the jewel (girdle) to the extra culet at an angle of 41° (for diamonds).
U.S. Pat. No. 5,072,549 to Johnston discloses a method of cutting facets on a gemstone, as well as the resulting stone, wherein facets are cut which produce a five-legged star which appears beneath the gem table. The product produced by this method comprises a pavilion having thirty facets and fifty edges, a crown having twenty-one facets and thirty-five facets, and a five-sided girdle.
U.S. Pat. Nos. 3,286,486 and 3,585,764 to Huisman et al disclose a brilliant-cut diamond having a pavilion formed of seventy-two facets and a total of one hundred and six overall. In the pavilion, there are eight kite-shaped (main pavilion) facets at 41° relative to the horizontal girdle plane, sixteen kite-shaped facets at 45°-47° relative to the girdle plane, sixteen star or diamond shaped facets at 53° to 54° from the girdle plane and 32 triangular facets at 58°-60relative to the girdle plane. As such, the pavilion defines a tapering upper area ranging from 58°-60° to 41° at the base thereof. The sixteen kite-shaped facets, although not beginning at the girdle, appear to extend along roughly half of the pavilion. Stones cut in accordance with the Huisman patents are not of higher yield, however, because the star and half of necessity facets are added after the bottom pavilion facets have already been cut.
As a result of the physical principles discussed above, varying the proportions of the facets of the stone will effect the appearance of the stone. At present, the gem industry has accepted the theory that the optimal angle of the base facets is roughly 41°. It has been stated by one well-known authority on the subject that deviation of 0.25% from that angle will dramatically affect the appearance of the stone. However, the inventors herein have discovered, in the process of attempting to increase the yield for cut stones, that, by blocking the stone in a certain “manner” using the technique of this invention, virtually the same visual characteristics can be obtained while also obtaining upwards of a 15% greater yield than has been available with existing techniques.
As used herein, the term “diamond” refers to both natural and man-made diamonds.